A class of proteins now has been identified that is competent to act as true chondrogenic tissue morphogens. That is, these proteins are able, on their own, to induce the proliferation and differentiation of progenitor cells into functional bone, cartilage, tendon, and/or ligamentous tissue. This class of proteins, referred to herein as “osteogenic proteins” or “morphogenic proteins” or “morphogens,” includes members of the family of bone morphogenetic proteins (BMPs) which were initially identified by their ability to induce ectopic, endochondral bone morphogenesis. The osteogenic proteins generally are classified in the art as a subgroup of the TGF-β superfamily of growth factors (Hogan (1996) Genes & Development 10:1580-1594). Members of the morphogen family of proteins include the mammalian osteogenic protein-1 (OP-1, also known as BMP-7, and the Drosophila homolog 60A), osteogenic protein-2 (OP-2, also known as BMP-8), osteogenic protein-3 (OP-3), BMP-2 (also known as BMP-2A or CBMP-2A, and the Drosophila homolog DPP), BMP-3, BMP-4 (also known as BMP-2B or CBMP-2B), BMP-5, BMP-6 and its murine homolog Vgr-1, BMP-9, BMP-10, BMP-11, BMP-12, GDF3 (also known as Vgr2), GDF8, GDF9, GDF10, GDF11, GDF12, BMP-13, BMP-14, BMP-15, GDF-5 (also known as CDMP-1 or MP52), GDF-6 (also known as CDMP-2), GDF-7 (also known as CDMP-3), the Xenopus homolog Vg1 and NODAL, UNIVIN, SCREW, ADMP, and NEURAL. Members of this family encode secreted polypeptide chains sharing common structural features, including processing from a precursor “pro-form” to yield a mature polypeptide chain competent to dimerize and containing a carboxy terminal active domain, of approximately 97-106 amino acids. All members share a conserved pattern of cysteines in this domain and the active form of these proteins can be either a disulfide-bonded homodimer of a single family member or a heterodimer of two different members (see, e.g., Massague (1990) Annu. Rev. Cell Biol. 6:597; Sampath, et al. (1990) J. Biol. Chem. 265:13198). See also, U.S. Pat. No. 5,011,691; U.S. Pat. No. 5,266,683, Ozkaynak et al. (1990) EMBO J. 2: 2085-2093, Wharton et al. (1991) PNAS n:9214-9218), (Ozkaynak (1992) J. Biol. Chem. 267:25220-25227 and U.S. Pat. No. 5,266,683); (Celeste et al. (1991) PNAS 87:9843-9847); (Lyons et al. (1989) PNAS 86:4554-4558). These disclosures describe the amino acid and DNA sequences, as well as the chemical and physical characteristics, of these osteogenic proteins. See also, Wozney et al. (1988) Science 242:1528-1534); BMP 9 (WO93/00432, published Jan. 7, 1993); DPP (Padgett et al. (1987) Nature 325:81-84; and Vg-1 (Weeks (1987) Cell 51:861-867).
Thus true osteogenic proteins capable of inducing the above-described cascade of morphogenic events resulting in endochondral bone formation, have now been identified, isolated, and cloned. Whether naturally-occurring or synthetically prepared, these osteogenic factors, when implanted in a mammal in association with a matrix or substrate that allows attachment, proliferation and differentiation of migratory progenitor cells, can induce recruitment of accessible progenitor cells and stimulate their proliferation, thereby inducing differentiation into chondrocytes and osteoblasts, and further inducing differentiation of intermediate cartilage, vascularization, bone formation, remodeling, and, finally, marrow differentiation. Furthermore, numerous practitioners have demonstrated the ability of these osteogenic proteins, when admixed with either naturally-sourced matrix materials such as collagen or synthetically-prepared polymeric matrix materials, to induce bone formation, including endochondral bone formation, under conditions where true replacement bone otherwise would not occur. For example, when combined with a matrix material, these osteogenic proteins induce formation of new bone in large segmental bone defects, spinal fusions, and fractures.
Naturally-sourced matrices, such as collagen, can be replaced with inert materials such as plastic, but plastic is not a suitable substitute since it does not resorb and is limited to applications requiring simple geometric configurations. To date, biodegradable polymers and copolymers have also been used as matrices admixed with osteogenic proteins for repair of non-union defects. While such matrices may overcome some of the above-described insufficiencies, use of these matrices necessitates determination and control of features such as polymer chemistry, particle size, biocompatibility and other particulars critical for operability. For example, pores must be formed in the polymer in a manner which ensures adsorption of protein into the matrix and biodegradation of the matrix. Prior to use of the polymeric matrix, therefore, it is necessary to undergo the extra step of treating the polymer to induce the formation of pores of the appropriate size.
Standard osteogenic devices, which include either collagen or polymer matrices in admixture with osteogenic protein, lend themselves less amenable to manipulation during surgery. Standard osteogenic devices often have a dry, sandy consistency and can be washed away whenever the defect site is irrigated during surgery, and/or by blood and/or other fluids infiltrating the site post-surgery. The addition of certain materials to these compositions can aid in providing a more manageable composition for handling during surgery. U.S. Pat. Nos. 5,385,887; 5,520,923; 5,597,897 and International Publication WO 95/24210 describe compositions containing a synthetic polymer matrix, osteogenic protein, and a carrier for such a purpose. Such compositions have been limited, however, to synthetic polymer matrices because of a desire to overcome certain alleged adverse immunologic reactions contemplated associated with other types of matrices especially biologically-derived matrices, including some forms of collagen. These compositions, therefore, suffer from the same feasibility concerns for optimizing polymer chemistry, particle size, biocompatibility, etc., described above.
Needs remain for compositions and methods for repairing bone and cartilage defects which provide greater ease in handling during surgery and which do not rely on synthetic polymer matrices. Needs also remain for methods and compositions that can enhance the rate and quality of new bone and cartilage formation.
Accordingly, it is an object of the instant invention to provide improved osteogenic devices and methods of use thereof for repairing bone defects, cartilage defects and/or osteochondral defects that: are easier to manipulate during surgery; circumvent the concerns of polymer chemistry, particle size and biocompatibility associated with the use of synthetic polymer matrices; and, which permit accelerated bone formation and more stable cartilage repair using lower doses of osteogenic protein than can be achieved using devices and methods now in the art. It is a further object of the instant invention to provide osteogenic devices and methods of use thereof for repairing non-healing, non-union defects and for promoting articular cartilage repair in chondral or osteochondral defects. Yet another object of the instant invention is to provide devices and methods for repair of bone and cartilage defects without surgical intervention. These and other objects, along with advantages and features of the invention disclosed herein, will be apparent from the description, drawings and claims that follow.